1. Field of the Invention
The present invention relates to an actuator, and particularly, to an actuator which is driven by using magnetism.
2. Description of the Related Art
An optical system having a focusing and a zooming function, has hitherto required a mechanism for moving a lens in a lens barrel in an optical axis direction. As a mechanism for moving the lens, for example, a mechanism which moves the lens by controlling passing of electricity to an actuator which has been installed in an endoscope has been proposed, As an example of such mechanism, an image pickup apparatus for an endoscope shown in Japanese Patent Application Laid-open Publication No. 2004-129950 has been proposed.
FIG. 3 shows a cross-sectional view of a structure according to a conventional technology. Inside an image pickup element frame 20, shape memory alloys 27 and 28 as driving means (actuators) of which, an entire length is extended due to heating by passing electricity are provided. An interior of a shell 19, and an image pickup optical frame 18, and the image pickup element frame 20 are connected by the shape memory alloys 27 and 28.
Based on a pressing operation of an operating section 29, a contact point 30 is put ON/OFF and electricity is passed and stopped. Accordingly, it is possible to adjust a supply of an electric current for heating, to the shape memory alloys 27 and 28. As a result of this, it is possible to change relative positions of the image pickup optical frame 18 and the image pickup element frame 20.
However, an amount of displacement of the actuator is restricted according to a length of the shape memory alloy. Therefore, an amount of displacement of the actuator which is disposed at an interior of a hard portion of an endoscope becomes small. Consequently, it is not possible to make substantial an amount of lens movement. Accordingly, a degree of freedom of optical designing becomes low.
Moreover, in the endoscope, airtightness of a structure including a structure of a surrounding of an image pickup apparatus and a surrounding of the actuator has been sought from a point of view of cleaning etc. It is desirable that the airtightness is as high as possible.